// Copyright © 2022 siddharth ravikumar <s@ricketyspace.net>
// SPDX-License-Identifier: ISC
package challenge
import (
"bufio"
"fmt"
"math/big"
"net"
"os"
"ricketyspace.net/cryptopals/lib"
)
func C35(args []string) {
if len(args) < 2 {
fmt.Println("Usage: cryptopals -c 35 ENTITY PORT [S-PORT] [G]")
return
}
entity := args[0]
if entity == "attacker" && len(args) != 4 {
fmt.Println("Usage: cryptopals -c 35 attacker PORT S-PORT G")
fmt.Println("\n G should be '1', 'p' or 'p-1'")
return
}
port, err := lib.StrToNum(args[1])
if err != nil {
fmt.Println("Port invalid")
return
}
if port < 12000 {
fmt.Println("Error: port number must be >= 12000")
return
}
sport := 0
gtype := ""
if entity == "attacker" {
sport, err = lib.StrToNum(args[2])
if err != nil {
fmt.Println("S-Port invalid")
return
}
if sport < 12000 {
fmt.Println("Error: port number must be >= 12000")
return
}
gtype = lib.StripSpaceChars(args[3])
if gtype != "1" && gtype != "p" && gtype != "p-1" {
fmt.Println("Error: G is invalid")
return
}
}
// Cipher functions.
//
// Pack a cipher and it's iv into packet.
cipherPacketEncode := func(cipher, iv []byte) string {
packet := append(cipher, iv...)
return lib.BytesToHexStr(packet)
}
// Unpack packet into cipher and iv.
cipherPacketDecode := func(packet string) (cipher, iv []byte) {
stream := lib.HexStrToBytes(packet)
cipher = stream[0 : len(stream)-16]
iv = stream[len(stream)-16:]
return cipher, iv
}
// Encipher using AES-CBC.
encipher := func(skey *big.Int, msg string) (string, error) {
// Make key out of DH sesssion key.
sha1 := lib.Sha1{}
sha1.Init([]uint32{})
sha1.Message(skey.Bytes())
skeyb := sha1.Hash()
if len(skeyb) < 16 {
// Pad it to 16 bytes.
skeyb = append(skeyb, make([]byte, 16-len(skeyb))...)
}
k := skeyb[0:16]
// Make initialization vector.
iv, err := lib.RandomBytes(16)
if err != nil {
return "", err
}
// Encrypt msg using AES-CBC
cipher := lib.AESEncryptCBC([]byte(msg), k, iv)
// Pack encrypted message in a format that can be sent
// over the wire.
packet := cipherPacketEncode(cipher, iv)
// Return packed encrypted message.
return packet, nil
}
// Decipher using AES-CBC.
decipher := func(skey *big.Int, packet string) (string, error) {
// Make key out of DH sesssion key.
sha1 := lib.Sha1{}
sha1.Init([]uint32{})
sha1.Message(skey.Bytes())
skeyb := sha1.Hash()
if len(skeyb) < 16 {
// Pad it to 16 bytes.
skeyb = append(skeyb, make([]byte, 16-len(skeyb))...)
}
k := skeyb[0:16]
// Decode packet
cipher, iv := cipherPacketDecode(packet)
// Decrypt message.
msg, err := lib.AESDecryptCBC(cipher, k, iv)
if err != nil {
return "", err
}
return string(msg), nil
}
// Server handling.
//
// Do DH handshake with client and return DH session key.
serverDHHandshake := func(conn net.Conn) (*big.Int, error) {
// Read p+g packet from client.
packet, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
return nil, err
}
// Remove newline character from packet.
packet = packet[:len(packet)-1]
// Try to read DH paramters from packet.
params := lib.StrSplitAt('+', packet)
if len(params) != 2 {
return nil, lib.CPError{Err: "DH paramters invalid"}
}
// Try make DH for this client connection.
dh, ok := lib.NewDH(params[0], params[1])
if !ok {
return nil, lib.CPError{Err: "DH initialization failed"}
}
// Send ACK to client.
fmt.Fprintf(conn, "ACK\n")
// Wait and get client's DH public key
packet, err = bufio.NewReader(conn).ReadString('\n')
if err != nil {
return nil, err
}
// Remove newline character.
packet = packet[:len(packet)-1]
// Parse client's DH public key.
cPub, ok := new(big.Int).SetString(lib.StripSpaceChars(packet), 10)
if !ok {
return nil, lib.CPError{Err: "DH public key invalid"}
}
// Send server's DH public key for this connection.
fmt.Fprintf(conn, "%v\n", dh.Pub())
// Return DH session key.
return dh.SharedSecret(cPub), nil
}
// Handle connection from a client.
serverHandleConn := func(conn net.Conn) {
defer conn.Close()
// Do DH handshake.
skey, err := serverDHHandshake(conn)
if err != nil {
fmt.Printf("DH Handshake failed [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
fmt.Printf("Made secure connection with %v\n", conn.RemoteAddr())
// Enter read-echo loop.
for {
packet, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
fmt.Printf("Closed connection to [%v]\n",
conn.RemoteAddr())
return
}
// Remove newline character.
packet = packet[:len(packet)-1]
// Decipher packet.
msg, err := decipher(skey, packet)
if err != nil {
fmt.Printf("Message decryption failed for [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
fmt.Printf("Received from [%v]: '%v'\n", conn.RemoteAddr(), msg)
// Make msg to client.
msg = fmt.Sprintf("-> %s", msg)
// Encrypt and echo back message.
cpacket, err := encipher(skey, msg)
if err != nil {
fmt.Printf("Message encryption failed for [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
// Send message to client.
fmt.Fprintf(conn, "%s\n", cpacket)
}
}
// Start "secure" echo server.
serverSpawn := func() {
p := fmt.Sprintf(":%d", port)
ln, err := net.Listen("tcp", p)
if err != nil {
fmt.Printf("Server listen error: %v\n", err)
return
}
for {
fmt.Println("Waiting for connection...")
conn, err := ln.Accept()
if err != nil {
fmt.Printf("Server accept error: %v", err)
}
go serverHandleConn(conn)
}
}
// Client handling.
//
// Try to make secure connection with server using DH and
// return server's DH public key.
clientSecureConnToServer := func() (net.Conn, *big.Int, error) {
// Try to connect to server.
addr := fmt.Sprintf(":%d", port)
conn, err := net.Dial("tcp", addr)
if err != nil {
return conn, nil, err
}
// Initialize DH.
p := lib.StripSpaceChars(
`ffffffffffffffffc90fdaa22168c234c4c6628b80dc1cd129024
e088a67cc74020bbea63b139b22514a08798e3404ddef9519b3cd
3a431b302b0a6df25f14374fe1356d6d51c245e485b576625e7ec
6f44c42e9a637ed6b0bff5cb6f406b7edee386bfb5a899fa5ae9f
24117c4b1fe649286651ece45b3dc2007cb8a163bf0598da48361
c55d39a69163fa8fd24cf5f83655d23dca3ad961c62f356208552
bb9ed529077096966d670c354e4abc9804f1746c08ca237327fff
fffffffffffff`)
g := "2"
dh, ok := lib.NewDH(p, g)
if !ok {
return conn, nil, lib.CPError{Err: "DH initialization failed"}
}
// Make DH packet: p+g
packet := fmt.Sprintf("%v+%v", p, g)
// Sent DH packet to server.
fmt.Fprintf(conn, "%s\n", packet)
// Wait and try to get ACK from server.
spacket, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
return conn, nil, err
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
if spacket != "ACK" {
return conn, nil, lib.CPError{Err: "ACK failed"}
}
// Send DH public key to server.
fmt.Fprintf(conn, "%v\n", dh.Pub())
// Get server's DH public key.
spacket, err = bufio.NewReader(conn).ReadString('\n')
if err != nil {
return conn, nil, err
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
// Parse server's DH public key.
sPub, ok := new(big.Int).SetString(lib.StripSpaceChars(spacket), 10)
if !ok {
return conn, nil, lib.CPError{Err: "Server's DH key invalid"}
}
// Return server connection and DH session key.
return conn, dh.SharedSecret(sPub), nil
}
// Start the client.
clientSpawn := func() {
// Make a secure connection to server.
conn, skey, err := clientSecureConnToServer()
if err != nil {
fmt.Printf("Unable to establish secure connection: %v\n", err)
return
}
defer conn.Close()
fmt.Printf("Made secure connection with %v\n", conn.RemoteAddr())
// Enter write loop.
for {
// Read message from stdin.
fmt.Printf("> ")
msg, err := bufio.NewReader(os.Stdin).ReadString('\n')
if err != nil {
fmt.Printf("Read error: %v\n", err)
return
}
// Remove newline character.
msg = msg[:len(msg)-1]
// Encrypt message.
packet, err := encipher(skey, msg)
if err != nil {
fmt.Printf("Encryption error: %v\n", err)
return
}
// Send message to server.
fmt.Fprintf(conn, "%s\n", packet)
// Read response from server.
spacket, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
fmt.Printf("Server closed connection\n")
return
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
// Decipher packet from server.
smsg, err := decipher(skey, spacket)
if err != nil {
fmt.Printf("Message decryption failed: %v\n", err)
return
}
// Barf server's response.
fmt.Printf("%s\n", smsg)
}
}
// Attacker handling.
//
// Slurp DH params from client.
attackerSlurpDHParams := func(conn net.Conn) ([]string, error) {
// Read DH packet from client.
packet, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
return []string{}, err
}
// Remove newline character from packet.
packet = packet[:len(packet)-1]
// Try to read DH paramters from packet.
params := lib.StrSplitAt('+', packet)
if len(params) != 2 {
return []string{}, lib.CPError{Err: "DH paramters invalid"}
}
// Try make a DH from params.
_, ok := lib.NewDH(params[0], params[1])
if !ok {
return []string{}, lib.CPError{Err: "DH initialization failed"}
}
return params, nil
}
// Return DH param `g` based on gtype.
attackerGetDHG := func(p string) (string, *big.Int, bool) {
if gtype == "1" {
return "1", new(big.Int).SetInt64(1), true
}
// Convert string `p` to big.Int.
pi, ok := new(big.Int).SetString(p, 16)
if !ok {
return "", nil, false
}
if gtype == "p" {
return p, pi, true
}
if gtype != "p-1" {
return "", nil, false
}
// gtype is "p-1"; make it.
pi.Sub(pi, new(big.Int).SetInt64(1))
return fmt.Sprintf("%x", pi), pi, true
}
// Try to make a connection with the server using DH and
// return serve'rs DH public key.
attackerSecureConnToServer := func(p, g string) (net.Conn, *big.Int, error) {
// Try to connect to server.
addr := fmt.Sprintf(":%d", sport)
conn, err := net.Dial("tcp", addr)
if err != nil {
return conn, nil, err
}
// Initialize DH.
dh, ok := lib.NewDH(p, g)
if !ok {
return conn, nil, lib.CPError{Err: "DH initialization failed"}
}
// Make DH packet: p+g
packet := fmt.Sprintf("%v+%v", p, g)
// Sent DH packet to server.
fmt.Fprintf(conn, "%s\n", packet)
// Wait and try to get ACK from server.
spacket, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
return conn, nil, err
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
if spacket != "ACK" {
return conn, nil, lib.CPError{Err: "ACK failed"}
}
// Send DH public key to server.
fmt.Fprintf(conn, "%v\n", dh.Pub())
// Get server's DH public key.
spacket, err = bufio.NewReader(conn).ReadString('\n')
if err != nil {
return conn, nil, err
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
// Parse server's DH public key.
sPub, ok := new(big.Int).SetString(lib.StripSpaceChars(spacket), 10)
if !ok {
return conn, nil, lib.CPError{Err: "Server's DH key invalid"}
}
// Return server connection and server's DH public key.
return conn, dh.SharedSecret(sPub), nil
}
// Handle connection from a client.
attackerHandleConn := func(conn net.Conn) {
defer conn.Close()
// Read DH params from client.
dhParams, err := attackerSlurpDHParams(conn)
if err != nil {
fmt.Printf("Error: %v\n", err)
return
}
// DH params for the server.
p := dhParams[0]
g, gi, ok := attackerGetDHG(p)
if !ok {
fmt.Println("Error: Unable to get DH param 'g'")
return
}
sconn, skey, err := attackerSecureConnToServer(p, g)
if err != nil {
fmt.Printf("Error: %v\n", err)
return
}
defer sconn.Close()
// Send ACK to client.
fmt.Fprintf(conn, "ACK\n")
// Wait and get client's DH public key
packet, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
fmt.Println("Error: Unable to read client's DH public key")
return
}
// Remove newline character.
packet = packet[:len(packet)-1]
// Parse client's DH public key.
_, ok = new(big.Int).SetString(lib.StripSpaceChars(packet), 10)
if !ok {
fmt.Println("Error: client DH public key invalid")
return
}
// Send server's session key as public key to client.
fmt.Fprintf(conn, "%v\n", skey)
// Client session key.
ckey := new(big.Int).Set(skey)
ckeyAlt := new(big.Int)
ckeyConfirmed := true
if gtype == "p-1" {
// ckey can be 1 or p-1. Set ckeyAlt to p-1 if
// ckey is 1; 1 otherwise.
ckeyConfirmed = false
if ckey.Cmp(new(big.Int).SetInt64(1)) == 0 {
ckeyAlt.Set(gi)
} else {
ckeyAlt.Set(new(big.Int).SetInt64(1))
}
}
// Enter mitm loop
for {
// Read from client.
packet, err := bufio.NewReader(conn).ReadString('\n')
if err != nil {
fmt.Printf("Closed connection to [%v]\n",
conn.RemoteAddr())
return
}
// Remove newline character.
packet = packet[:len(packet)-1]
// Decipher packet.
if !ckeyConfirmed {
_, err = decipher(ckey, packet)
if err != nil {
ckey = ckeyAlt
ckeyConfirmed = true
}
}
msg, err := decipher(ckey, packet)
if err != nil {
fmt.Printf("Message decryption failed for [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
fmt.Printf("Received from client [%v]: '%v'\n",
conn.RemoteAddr(), msg)
// Encrypt and forward message to server.
spacket, err := encipher(skey, msg)
if err != nil {
fmt.Printf("Message encryption failed for [%v]: %v\n",
sconn.RemoteAddr(), err)
return
}
// Send message to server.
fmt.Fprintf(sconn, "%s\n", spacket)
// Read encrypted message from server.
spacket, err = bufio.NewReader(sconn).ReadString('\n')
if err != nil {
fmt.Printf("Closed connection to [%v]\n",
sconn.RemoteAddr())
return
}
// Remove newline character.
spacket = spacket[:len(spacket)-1]
// Decipher packet.
msg, err = decipher(skey, spacket)
if err != nil {
fmt.Printf("Message decryption failed for [%v]: %v\n",
sconn.RemoteAddr(), err)
return
}
fmt.Printf("Received from server [%v]: '%v'\n",
sconn.RemoteAddr(), msg)
// Encrypt and echo back message.
cpacket, err := encipher(ckey, msg)
if err != nil {
fmt.Printf("Message encryption failed for [%v]: %v\n",
conn.RemoteAddr(), err)
return
}
// Send message to client.
fmt.Fprintf(conn, "%s\n", cpacket)
}
}
// Start (mitm) attacker server.
attackerSpawn := func() {
p := fmt.Sprintf(":%d", port)
ln, err := net.Listen("tcp", p)
if err != nil {
fmt.Printf("Attacker listen error: %v\n", err)
return
}
for {
fmt.Println("Waiting for connection...")
conn, err := ln.Accept()
if err != nil {
fmt.Printf("Attacker accept error: %v", err)
}
go attackerHandleConn(conn)
}
}
// Take action based on entity.
switch {
case entity == "server":
serverSpawn()
case entity == "client":
clientSpawn()
case entity == "attacker":
attackerSpawn()
default:
fmt.Println("Error: Uknown entity")
}
}
// Output:
//
// Part I:
//
// $ ./cryptopals -c 35 server 12000
// Waiting for connection...
// Waiting for connection...
// Made secure connection with 127.0.0.1:40557
// Received from [127.0.0.1:40557]: 'Put this together while listening to'
// Received from [127.0.0.1:40557]: 'Kara Swisher's Sway.'
//
// $ ./cryptopals -c 35 client 12000
// Made secure connection with 127.0.0.1:12000
// > Put this together while listening to
// -> Put this together while listening to
// > Kara Swisher's Sway.
// -> Kara Swisher's Sway.
// > ^C
//
// Part II:
//
// https://ricketyspace.net/cryptopals/c35.webm
//
// $ ./cryptopals -c 35 server 12000
// Waiting for connection...
// Waiting for connection...
// Made secure connection with 127.0.0.1:27477
// Received from [127.0.0.1:27477]: 'If the red slayer think he slays,'
// Closed connection to [127.0.0.1:27477]
// Waiting for connection...
// Made secure connection with 127.0.0.1:46947
// Received from [127.0.0.1:46947]: 'Or if the slain think he is slain,'
// Closed connection to [127.0.0.1:46947]
// Waiting for connection...
// Made secure connection with 127.0.0.1:42735
// Received from [127.0.0.1:42735]: 'They know not well the subtle ways'
// Received from [127.0.0.1:42735]: 'I keep, and pass, and turn again.'
// Closed connection to [127.0.0.1:42735]
// ^C
//
// $ ./cryptopals -c 35 attacker 12001 12000 1
// Waiting for connection...
// Waiting for connection...
// Received from client [127.0.0.1:12597]: 'If the red slayer think he slays,'
// Received from server [127.0.0.1:12000]: '-> If the red slayer think he slays,'
// Closed connection to [127.0.0.1:12597]
// ^C
// ada$ ./cryptopals -c 35 attacker 12001 12000 p
// Waiting for connection...
// Waiting for connection...
// Received from client [127.0.0.1:47227]: 'Or if the slain think he is slain,'
// Received from server [127.0.0.1:12000]: '-> Or if the slain think he is slain,'
// Closed connection to [127.0.0.1:47227]
// ^C
// ada$ ./cryptopals -c 35 attacker 12001 12000 p-1
// Waiting for connection...
// Waiting for connection...
// Received from client [127.0.0.1:9193]: 'They know not well the subtle ways'
// Received from server [127.0.0.1:12000]: '-> They know not well the subtle ways'
// Received from client [127.0.0.1:9193]: 'I keep, and pass, and turn again.'
// Received from server [127.0.0.1:12000]: '-> I keep, and pass, and turn again.'
// Closed connection to [127.0.0.1:9193]
// ^C
//
// $ ./cryptopals -c 35 client 12001
// Made secure connection with 127.0.0.1:12001
// > If the red slayer think he slays,
// -> If the red slayer think he slays,
// > ^C
// ada$ ./cryptopals -c 35 client 12001
// Made secure connection with 127.0.0.1:12001
// > Or if the slain think he is slain,
// -> Or if the slain think he is slain,
// > ^C
// ada$ ./cryptopals -c 35 client 12001
// Made secure connection with 127.0.0.1:12001
// > They know not well the subtle ways
// -> They know not well the subtle ways
// > I keep, and pass, and turn again.
// -> I keep, and pass, and turn again.
// > ^C
